Forbes LogoOdds are, if you're 50 or older, you know you should be exercising. But in all likelihood, you're probably spending more time on the couch or in the car than on the treadmill or hiking trail.

Only just over one-fourth of the 50-plus crowd are engaged in some type of physical activity in their leisure time, including 29.3% of 50- to 64-year-olds, 26.4% of 65- to 74-year-olds and 15.7% of those 75 and over, according to a 2006 report from the American Association of Retired Persons (AARP). Physical activity constitutes light to moderate exercise for 30 minutes or more, five times a week, or vigorous exercise for 20 minutes or more, three times a week.

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This kind of sedentary lifestyle costs you in more ways than you might think. Older adults already account for close to one-third of total U.S. health care expenditures, or $300 billion a year, says the National Center for Chronic Disease Prevention and Health Promotion. And as the oldest of the 79 million baby boomers turn 62 this year—and struggle to stay fit—those costs are expected to rise.

But experts say that price tag could be cut if more boomers are willing to get moving, since a routine of moderate physical activity can reduce the risk of falling, fracturing bones and developing conditions such as high blood pressure and diabetes.

While most boomers facing retirement know the importance of planning financially for the coming 20 to 40 years, they'd be a lot better off if they also put that kind of time and energy into creating a fitness plan, says Gregory Florez, founder and CEO of health coaching provider

"If your health fails, it doesn't matter if you have a house in the Hamptons," Florez says. "Your health truly must become a top priority right now."

Graduation Time
Much like seniors graduating from college, most new retirees don't know what they're going to do with the rest of their lives, and have trouble coping with the transition, says Nancy Schlossberg, professor emerita at the University of Maryland and author of Retire Smart, Retire Happy: Finding Your True Path in Life. Suddenly, they find themselves at home, facing days lacking structure and possibly experiencing a touch of post-career depression.

While people tend to dreamily say they want to spend their retirements traveling the world, in reality, many retirees have trouble getting off the couch.

Luckily, you don't need to be a fitness expert to develop a workout routine that suits this new stage of your life. The key to a healthy retirement is just as much about setting goals and knowing what motivates you as it is about exercise.

Getting To Work
If you're just about to retire, take advantage of any health assessment programs your company offers, advises Florez. Make an appointment for a complete physical, find out your numbers—from blood pressure to cholesterol—and ask for a stress test to see how well your heart handles work.

While you're at it, tell your doctor you're thinking of starting an exercise routine, and ask if there are any kinds of activities or intensity levels you should avoid.

Next, think about your workout style and what kind of exercise program you're most likely to follow. If, every time you run, you end up injured—or with a mind full of good reasons to stop—try something new.

And if you've always loved tennis or have a fantasy of becoming a single-digit-handicap golfer, look at your retirement as a time to indulge your fitness passions. Join a club that will allow you to hit the links as often as you want, or start planning that two-week biking trip through the French countryside.

Whatever fitness routine you settle on, Schlossberg recommends including a friend. Some days, you're just not going to be in the mood to attend your water aerobics class. But it's possible that knowing your buddy will be there, or just the general camaraderie, will motivate you to go anyway.

For those retirees who really can't stand exercise, Colin Milner, CEO of the International Council on Active Aging, suggests thinking small. Instead of forcing yourself to run a certain distance five times a week, try walking. Create a routine that includes the minimum amount of activity you need to stay healthy, and once you've got the hang of it, build on it.

Exercise may not be your favorite part of your retirement, but without it, you're jeopardizing the quality of your golden years.

"At the end of the day," Milner says, "it has nothing to do with whether you like exercise or not. It's about whether you want to enjoy the things around you, like your grandkids, and whether you want to stay independent."